Dendritic action potentials and computation in human layer 2/3 cortical neurons

Abstract

The active electrical properties of dendrites shape neuronal input and output and are fundamental to brain function. However, our knowledge of active dendrites has been almost entirely acquired from studies of rodents. In this work, we investigated the dendrites of layer 2 and 3 (L2/3) pyramidal neurons of the human cerebral cortex ex vivo. In these neurons, we discovered a class of calcium-mediated dendritic action potentials (dCaAPs) whose waveform and effects on neuronal output have not been previously described. In contrast to typical all-or-none action potentials, dCaAPs were graded; their amplitudes were maximal for threshold-level stimuli but dampened for stronger stimuli. These dCaAPs enabled the dendrites of individual human neocortical pyramidal neurons to classify linearly nonseparable inputs—a computation conventionally thought to require multilayered networks.

Non-linear Neurons with Human-like Apical Dendrite Activations

“…In contrast to Rosenblatt's perceptron and ADALINE, we propose an artificial neuron that has two input branches, the basal branch and the apical tuft. The apical tuft is par-ticularly novel because it uses a novel activation function (Gidon et al, 2020) that can solve non-linearly separable problems.…”

“…segregated dendrites in the context of deep learning (Guerguiev et al, 2017) or memorizing sequences with active dendrites and multiple integration zones (Hawkins & Ahmad, 2016), to our knowledge, we are the first to propose an artificial pyramidal neuron that is inspired by the recent discovery of Gidon et al (2020). Different from previous studies, the apical tuft of our pyramidal neuron is equipped with the novel apical dendrite activation suggested by Gidon et al (2020). Furthermore, we integrate our pyramidal neuron into various deep neural architectures, showing its benefits over standard artificial neurons.…”

“…Furthermore, we integrate our pyramidal neuron into various deep neural architectures, showing its benefits over standard artificial neurons. We note that Gidon et al (2020) have not presented the pyramidal neuron in a computational scenario, hence we are the first modeling it computationally.…”

“…The activation function illustrated in Figure 1 and deduced from the experiments conducted by Gidon et al (2020) can be formally expressed as follows:…”

“…Electrical impulses are sent to the neuron through both kinds of dendrites and the impulse is passed down the axon, if an action potential occurs. Prior to Gidon et al (2020), it was thought that apical and basal dendrites had identical activation functions. This is because experiments were usually conducted on pyramidal neurons extracted from rodents.…”